3 Integrating across levels of analysis
In mammals and birds, homeostasis, the provision of a stable internal environment, includes keeping certain physiological variables, T b, cellular and extracellular water and blood glucose at near constant levels. T b of reptiles varies with T a, but reptiles can only function over a limited range of T b. Nevertheless, vertebrate species live successfully in deserts, which are arid, have low productivity and extremes of T a. Our approach to understanding animals’ physiological responses and genotypic adaptations linked to environmental features of deserts is study and integration of different levels of analysis, covering behaviour, anatomy, physiology and biochemistry. Grouping desert animals into evaders, evaporators and endurers is useful for our purpose. We describe just a few examples here, but the principles identified can help in interpreting data derived from other species.